Dynamics of Di(propylene glycol) Dibenzoate-d10 in Poly(vinyl acetate) by Solid-State Deuterium NMR

Deuterium solid-state NMR and temperature-modulated differential scanning calorimetry were used to probe the dynamics of the plasticizer di(propylene glycol) dibenzoate (DPGDB-d(10)) in mixtures with poly(vinyl acetate) (PVAc). The plasticizer, deuterated in the phenyl rings, was synthesized, and H-2 NMR spectra were obtained from PVAc samples with 10, 22, 27, and 37% deuterated plasticizer content as a function of temperature. The dynamics of the plasticizer in the plasticized polymer system were found to be heterogeneous with respect to different plasticizer molecules undergoing different motions. The experimental H-2 NMR line shapes were fitted using a set of simulated spectra obtained from the MXQET program. The simulations were based on the superposition of two types of motion: a two site jump motion, i.e, 180 degrees ring flips, plus isotropic motions. The presence of the polymer allowed more plasticizer molecules to undergo 180 degrees ring flips than in the bulk plasticizer. For the average of the log of the rate constants for the ring flips (< log k >) versus 1/temperature was linear with an apparent energy of activation of 75 kJ/mol for ring flips. From both NMR and TMDSC, the reduction in T-g was proportional to the amount of plasticizer added. In addition, the T(g)s of DPGDB-d(10)/PVAc as a function of plasticizer content were found to be similar to those of PVAc-d(3)/DPGDB as determined by NMR The NMR data for both the polymer and plasticizer and TMDSC data may be fit to a plasticization model of Jenkel and Heusch with an interaction parameter b = -0.53, suggesting that both species were sensitive to the same local environment.